The current invention has application to the field of grain production and plant pollination practices, including, but not limited to, economically significant grain crops such as maize (also called corn), soybeans, wheat, rice, sunflower, canola, sorghum, barley, and pearl millet. The term “grain production” as used in this disclosure is intended to mean commercial-scale grain production, using a minimum field size of 0.8 hectares (2 acres) of land for the production of said grain. A conventionally grown grain field is typically predominantly F1 plants that share genes in common from 2 inbred parents (although conventional grain will also have a small percentage of contaminant seed (not F1) in a standard bag of seed.). In other situations, the “top-cross” method is used for grain production. In contrast to the conventional field of F1 plants, top-cross grain uses a field that is a blend of a male sterile hybrid (˜93%) and a male fertile high oil pollinator germplasm (7%). Commercial grain production often relies upon field production of hybrid plants. Hybrid plants are the result of fertilization occurring from a male pollen source of one genetic background being crossed to the female reproductive organs of a plant with a different genetic background. Hybridity among crop plants generally gives a yield advantage in commercial production. Currently, maize, rice, sorghum, sunflower, and canola are the primary crops which take advantage of hybrid seed. Other grains are less commonly grown as hybrids, as is the case with soybean, wheat, barley, pearl millet and others.
For crops in which grain production is commonplace, current methods of producing grain vary slightly by species, but typically involve planting fields of the same seed variety to produce plants whose mature seeds will result in the desired grain. The plants in such fields are typically self-pollinated or pollinated by neighboring plants in the field. There may be some cross pollination from nearby fields of similar species.
For the purposes of this disclosure and its applicability to grain production, the term “self-pollen,” which is a single plant's own pollen, includes “sib-pollen,” which is pollen from sibling plants who share the same genetics. Likewise, the term “self-pollination” includes “sib-pollination.” which is pollination occurring with pollen from a sibling plant, and which has the same effect in the resulting grain as self-pollination. In a hybrid grain production field, all self-pollination and sib-pollination is effectively self-pollination in terms of the effect on the grain, which is a yield decrease (in comparison to outcrossing) and purity increase in the case of food corn. “Cross pollination,” for the purposes of this disclosure, refers to genetic exchange between inbreds or hybrids in adjacent and surrounding fields, not from plants within the same field. Thus, cross pollination is the introduction of pollen that is derived or sourced from separate locations that is genetically distinct from the pollen which will be shed from the plants within the grain production field.
The advantage of using hybrid seed for grain production is that hybrids are known to exhibit heterosis, which is expressed as hybrid vigour, meaning a stronger and more resilient plant. Heterosis also results in higher grain yields. This effect is sometimes referred to as xenia. (Stamp et al. (2002) Crop Sci. 42:1848-1856; Stamp et al. (2002) Maydica 47:127-134). Heterosis also occurs when an existing hybrid plant (created from 2 different parent plants) is fertilized with pollen from yet another plant, providing a subsequent boost in yield. Hybrid grain crops substantially out yield non-hybrid cultivars and also exhibit better response to fertilizers. However, conditions during the growing season vary from year to year and pressures caused by environmental challenges, disease outbreaks and insect infestations can significantly impact grain yield.
Theoretically, cross pollinating hybrids can provide a yield benefit by avoiding the in-breeding depression associated with self- or sib-pollination, or by creating new gene combinations that generate a heterotic response within the kernels. This response has been termed the ‘xenia effect.’ “Xenia can be defined as the effect of the pollen genes on the development of the fruit or the seeds.” (Bulant et al. ((2000) Crop Sci. 40: 182-188)
Numerous studies have shown the influence of the pollen source on the development of the kernel. Among the earliest demonstrations (Kiesselbach, T. A. (1926) Neb. Agric. Exp. Stn. Bull. 33:1-69; Kiesselbach. T. A. & W. H. Leonard (1932) J. Am. Sc. Agron. 24:517-523), Kiesselbach reported that relative to self-fertilization, cross fertilization increased kernel weights on average by 10.1% (11.8% for embryos, 10.4% for endosperm, and 3.2% for pericarp). Tsai and Tsai (Tsai, C. L. & C. Y. Tsai (1990) Crop Sci. 30: 804-808) showed an increase in grain yield of about 30% and in increase in kernel protein content of about 44% in an early hybrid when it was pollinated by a late hybrid. Using maize inbred lines with normal endosperm, Bulant et al. ((2000) Crop Sci. 40: 182-188) reported a relative advantage in weight of cross-fertilized to self-fertilized kernels as great as 13%. Breeding studies at South Dakota State University confirm that cross pollination of specific hybrids can increase kernel size and protein content, and that cross pollination between hybrids of similar maturity accounts for 40 to 60% of kernels formed in mixed stands (Wicks III, Z., (1994) Proc. Annual Corn and Sorghum Res. Conf. 4.
The development of the kernels can be altered by cross pollination (Tsai, C. L. & C. Y. Tsai (1990) Crop Sci. 30: 804-808; Poneliet, C. G. and D. B. Egli, (1983) Crop Sci. 23:872-875). Poneliet and Egli (1983) showed that the duration of the effective filling period from cross-fertilization often was greater than that from self-fertilization. Pollen source also affects endosperm development in terms of protein content, amino acid profile, and translucency. (Pixley. K. V. and M. S. Bjarnason (1994) Crop Sci. 34:404-408: Bulant et al. (2000) Crop Sci. 40: 182-188). At 14 DAP, the advantage of cross-fertilization on average was 28.8% for starch content, 24.8% for ADP-glucose-pyrophosphorylase (EC 2.7.7.27) activity, and 24.1% for neutral invertase (EC 3.2.1.26) activity (Bulant et al. (2000) Crop Sci. 40: 182-188). Tsai et al. ((1991) J. Sci. Food Agric. 57: 163-174) modified P3732 endosperm through cross-pollination, which significantly increased kernel weight, kernel protein content and grain yield across a range of fertilizer N treatments. The additional nutrients translocated into developing kernels of P3732 cross-pollinated plants were mainly derived from increases in duration of dry matter production and N uptake by vegetative tissues (Tsai et al. (1991) J. Sci Food Agric. 57: 163-174). These well-established impacts on kernel composition are the basis for the top-cross method of producing high oil corn. The top-cross system for high oil corn grain production was a method used in the 1990s and early 2000s in which high oil was induced by planting a blend of a male sterile hybrid (˜93%) and a male fertile high oil pollinator germplasm (7%). The result was an increase in oil from about 3-4% for normal commodity grain, to about 6% for the high oil top-cross grain. The high oil grain brought a premium price per bushel at the grain elevator. (Thomison. P. R. et al. (2002) Agron. J. 94: 290-299.)
The extent of the xenia effect varies with the male and female genotype. The greater the genetic difference between the male pollen source and female, the greater the expected response to cross-pollination. (Leng, E. R., (1949) Agron. J. 41:555-558; Bulant, C. and A. Gallais, (1998) Crop Sci. 38: 1517-1525). The cross fertilization advantage was less for single-cross hybrids than for their inbred parents, and the advantage varies with the male. For crosses between inbreds, the advantage of cross fertilization was 13.8 and 14.5%, but only 2.5% for crosses made with their hybrid (Bulant. C. and A. Gallais, (1998) Crop Sci. 38: 1517-1525). Both pollen and maternal effects impact the response to cross pollination (Seka, D and I. Z. Cross (1995) Crop Sci. 35: 80-85; Seka. D. et al. (1995) Crop Sci. 35: 74-79).
Results of cross pollinations between hybrids observed by Bulant and Gallais (Bulant, C. and A. Gallais, (1998) Crop Sci. 38: 1517-1525) illustrate that cross fertilization can increase the sink strength of the whole ear and that the kernel mass benefit can be observed under unfavorable conditions. The positive xenia effects have been interpreted in terms of source-sink relationships. If the resources are limiting, the increase in sink strength leads to a greater average kernel weight with mixed fertilization than with pure self-fertilization. There was no relationship between the cross-fertilization advantage and the average seed weight of the self-fertilized female or male pollen source. Cross-fertilization advantage was beneficial for small kernels as well as for large kernels (Bulant, C. and A. Gallais, (1998) Crop Sci. 38: 1517-1525).
Pollination success is critical to grain yield. Grain yield is measured as the weight of grain per area of land measured at a given moisture content (for example, 15.5% moisture for corn). Low pollination rates result in poor grain yield. For this reason, grain producers typically rely upon self-pollination and pollination by neighboring plants in the field since they know that the pollination will occur during the correct window of time because the female components of the plant will be ready to receive the pollen. Unfortunately, self-pollination will not necessarily maximize grain yield and it is unable to account for changing conditions and stresses that may affect the plant during the growing season.
Accordingly, there is a need in the industry for an invention which allows for the improvement of grain yield, grain content, grain purity, grain characteristics, decreased contamination, or a combination of these attributes. The instant invention provides a method for the improvement of grain yields by intentionally cross-pollinating the plants producing the grain. In addition, the instant invention provides a method for the increase of grain size and the modification of grain constituents by means of specific cross-pollination with pollen from a different genetic background, the method for which also allows for real-time production decisions to address conditions at the time of pollination or to address production challenges. This method can also reduce undesirable contamination in the grain harvested from the field. The instant invention also provides a method of maximizing synchronous pollination with self- or sib-pollen, which provides for the reduction of contamination caused by undesirable cross-pollination, which is particularly applicable to the organic farming industry. These two methods can also be combined to both increase yield and modify grain size and constituents in the same grain field, while also reducing contamination.
The invention described herein would enable a 5% grain yield increase in corn (a conservative estimate), the annual value of this invention with 33% adoption, mostly on higher productivity land, would be $1.1 billion to the entire value chain in the U.S. alone. This is based on 2015 US corn production of 345 metric tons (U.S. Corn Growers Association (2016) World of Corn [online, retrieved on 2016 Jun. 13], Retrieved from the internet) and a corn commodity price of $185.04 per metric ton (Jun. 13, 2016 corn price [online, retrieved on 2016 Jun. 13] Retrieved from the internet) (Calculation: $185.04/MT×345 MM MT×5% yield increase×33% adoption). Likewise, the invention described herein could enable a 5% grain yield increase in rice, which would have an annual value, with 10% adoption, mostly by larger farmers on highly productive land, of $1.5 billion globally. This is based on 2013 global rice production of 746 MM metric tons (GeoHive (2016) [online] World: Rice Production in Metric Tonnes, retrieved on 2016 Jun. 20. Retrieved from the internet) and a rice commodity price of $408.91 per metric ton (May 2016 rough rice commodity price [online], retrieved from the internet on 2016 Jun. 23. Retrieved from the internet) (Calculation: $408.91/MT×746 MM MT×5% yield increase×10% adoption).